Updates to /status API

This patch returns additional data from the /status API call. Specifically, it
returns a worker list, the message broker connection status, the database
connection status, and the Pulp version (RHBZ #704184).

There is a small behavior change to include the resource manager and scheduler
as part of the worker heartbeat list. Previously, these were not included in
the list.
Would we ever want to put more information on these, perhaps DB host name or detected version, or whether SSL is being used? If so, it might be good to go ahead and make these JSON objects instead of bools so that we could add to them in a Y release instead of having to wait for an X release to change them. Even if we just make it a JSON object with only the key "connected" set to true/false, I think that's future-safe.

This isn't a blocker, so do what you prefer.